Percolation and clustering in supercritical aqueous fluids

Neutron diffraction data for pure supercritical water and supercritical mixtures of water and CO2 are analyzed by using the empirical potential structure refinement Monte Carlo simulation, and molecular configurations compatible with the experimental data are recorded. The analysis of the distribution functions of water cluster size in these fluids allows the identification of a percolation line, which separates gas-like states from liquid-like ones, in pure supercritical water. Solvation of CO2 in supercritical water inhibits cluster percolation, although the radial distribution functions show liquid-like behavior: this is likely to be due to the excess volume being localized around the CO2 molecules.